WO 98/38085 A1 discloses a continuous-flow machine having at least two rotors which are mounted such that they can rotate about a rotation axis in mutually opposite directions and on the outer side of which blades or vanes are arranged and having a shaft which is mounted such that it can rotate about the same rotation axis, and having a drive mechanism in the form of a transmission for converting a rotary movement of the shaft to rotary movements of the rotors in mutually opposite directions, that is to say contrarotation, and/or vice versa. In this case, the shaft runs along the rotation axis of the rotors and through it.
The continuous-flow machine can be used particularly advantageously for a marine-vessel propulsion system, for example a POD, in which the blades or vanes of the first rotor form a first propeller, and the blades or vanes of the second rotor form a second propeller, which propellers are driven by the shaft via the propulsion mechanism. The contrarotating second propeller partially redirects the lossy swirl of the propeller outlet flow from the first propeller and converts it to thrust. Mechanical torque compensation such as this improves the efficiency of the marine-vessel propulsion system.
By way of example, the shaft can in this case be driven by an electric motor or an internal combustion engine. The shaft torque is distributed by the drive mechanism between the two propellers, wherein the rotation speed of the shaft is advantageously chosen to be greater than the rotation speed of the two rotors. The drive mechanism therefore acts as a reduction transmission.
This is particularly advantageous in drive systems in which the shaft is driven by an electric motor, because the rotation speed of the electric motor may be higher than without a reduction transmission and, in consequence, the diameter of the electric motor can be reduced.
The continuous-flow machine can also be used particularly advantageously as a turbine, for example for driving a generator. The rotors then drive the shaft, in which case the rotation speeds of the at least two rotors are advantageously less than the rotation speed of the shaft. The drive mechanism then acts as a step-up transmission, as a result of which the torque to be transmitted by the shaft decreases.
The known continuous-flow machine is subject to the problem that the drive mechanism must be accommodated in the relatively small hub. This results in the hub being highly mechanically complex. The dense design furthermore leads to bearing problems and to problems in lubrication of the bearings, which may possibly adversely affect the reliability of the continuous-flow machine. In order to counteract this, the hub would need to be made larger, although this is disadvantageous from the fluid-dynamic point of view, and would destroy the efficiency advantages of the contrarotating arrangement.